Standard facsimile devices which operate only as facsimile machines connected directly to a telephone line are rapidly being replaced by devices which combine facsimile and/or digital scanning, copying and printing in one single unit. Note, e.g., U.S. Pat. Nos. 4,947,345 to Paradise; 3,597,071 to Jones; 5,038,218 to Matsumoto; 5,021,892 to Kita, et al.; and 4,623,244 to Andrews, et al. One class of these devices may conveniently be directly connected to a personal computer or workstation to provide printing, and to a telephone access line to provide facsimile transmission and receipt.
It is well known that control of the Tone Reproduction Curve (TRC) for a system can improve printing quality. In a standard document processing system, scanner and printer characteristics are known. Based on these factors, TRC is adjusted so that an incremental change in gray scale value of the image signal causes a similar change in the gray scale response at a printer. Typically this may be accomplished with a Look up Table (LUT) stored in a memory that maps gray value image signals from the system (typically from the scanner) to printer signals suitable for driving the printer. Other methods of accomplishing this function are well known. For a further discussion of TRC correction, note Digital Document Processing by H. Hou, John Wiley and Sons, 1983, pp. 100-103.
Facsimile devices present an unusual case in TRC correction, in that information about the ultimate printer driven by the image signals is typically not available. Destination devices (including multifunction machines) may include xerographic printers, thermal transfer printers, thermal paper printers, ink jet printers, etc. In standard practice, each of these printers would require a distinct TRC correction. While every printer model (in fact, every printer) might have a distinctive TRC, fortunately, each type of printer is broadly similar, e.g. ink jet printers have a TRC with a set of common characteristics. For facsimile transmission, a default TRC curve is assumed.
Facsimile protocols allow non standard facilities (NSF) or functions to be defined. Assuming that a calling fax and a called fax have a common NSF function, they can take advantage of proprietary features, even though not part of the CCITT standards protocols. See, Recommendation T.30 "Procedures for Document Facsimile Transmission in the General Switched Telephone Network", Melbourne 1988 (ITU). This is a commonly used practice for other functions such as compression.
References disclosed herein are incorporated by reference for their teachings.